1. Technical Field
The present invention relates to a projector incorporated with a laser light source as a light source.
2. Background Art
A projector for displaying an image on a screen has been spread as an image display device. Generally, a lamp light source is used in the projector. However, the lamp light source has drawbacks that the life is short, the color reproducing range is limited, the volume of the light source is large, and the light use efficiency is low.
A laser light source has been attempted to be used as a light source in a projector to solve the above drawbacks. Since the laser light source has a long life and a strong directionality, as compared with a lamp light source, the light use efficiency of the laser light source can be easily enhanced. Further, since the laser light source has monochromaticity, the laser light source has a wide color reproducing range, and is capable of displaying a clear image. Furthermore, since the laser light source can be miniaturized, as compared with a conventional light source, and serves as a point light source, optical components of the laser light source can also be miniaturized. In view of these merits, the laser light source may be applicable to a portable projector, which has not been proposed in the conventional art.
In a projector (hereinafter, called as a laser projector) incorporated with a laser light source, however, speckle noise resulting from high coherence of laser light has become a problem. The speckle noise is a fine grain noise perceived by viewer's eyes, resulting from coherence between scattered light when the laser light is scattered on a screen. Randomly-arranged grains of a size determined by the F-number of the viewer's eyes and the wavelength of a laser light source are perceived as the speckle noise. The speckle noise obstructs the viewer from viewing an image on a screen, and causes serious image degradation.
Heretofore, there has been proposed an approach of controlling the beam angle by an optical system, as an approach of reducing speckle noise. For instance, patent literature 1 proposes pixelation and speckle noise reduction by oscillating a foldable mirror. Patent literature 2 proposes reducing scintillation (speckle noise) by oscillating an optical axis of a projection optical system in a very small angle range.
However, since the above proposals are made considering speckle noise reduction in a lamp light source, an angle change amount is small, and a sufficient speckle noise removal effect is not obtained, if the above proposals are applied to a laser light source.
Patent literature 3 proposes driving an element in a projection optical system to correct handshake of a portable projector. Patent literature 3, however, may fail to remove speckle noise under a condition including a case that image projection is performed in a state that a portable projector is fixed.
As described above, there are some proposals relating to speckle noise removal in a projector. However, none of the proposals provides a sufficient speckle noise removal effect in a laser projector, and the proposals fail to remove speckle noise, utilizing a two-dimensional light modulator.
Patent literature 1: JP (tokuhyo) 2002-543455A
Patent literature 2: JP 2003-21806A
Patent literature 3: JP 2006-138939A